Fully dense consolidated-powder superalloys

ABSTRACT

Superalloys formed of consolidated powder, which are fully dense and have a composition by weight consisting essentially of about 0.01 to 0.5 percent carbon, about 5 to 30 percent cobalt, about 6 to 12 percent chromium, about 4 to 9 percent aluminum, about 0.5 to 6.5 percent titanium, about 8 to 12 percent aluminum plus titanium, about 1 to 8 percent molybdenum, and the balance nickel together with minor alloying ingredients and incidental impurities, are characterized by being readily workable as compared to conventional casting alloys of the same chemical composition which are too brittle and have too little ductility to hot work.

United States Patent Fletcher [4 Mar. 14, 1972 [54] FULLY DENSE CONSOLIDATED- POWDER SUPERALLOYS [72] Inventor: Stewart G. Fletcher, Latrobe, Pa.

[73] Assignee: Latrobe Steel Company, Latrobe, Pa.

[22] Filed: Feb. 18, 1970 [211 App]. No.: 12,422

52 us. Cl. ..75/171, 29/182, 75/05 BB, 75/05 0 51 1111.0 ..C22c 19/00 [58 Field of Search ..75/171, 170, 0.5 BB, 0.5 c; 148/32, 32.5; 29/182 [56] References Cited UNITED STATES PATENTS 3,524,144 8/1970 Parikh ..75/171 Primary Examiner-Richard 0. Dean Attomey-Fidler, Bradley, Patnaude & Lazo [57] ABSTRACT Superalloys formed of consolidated powder, which are fully dense and have a composition by weight consisting essentially of about 0.0! to 0.5 percent carbon, about 5 to 30 percent cobalt, about 6 to 12 percent chromium, about 4 to 9 percent aluminum, about 0.5 to 6.5 percent titanium, about 8 to 12 percent aluminum plus titanium, about 1 to 8 percent molybdenum, and the balance nickel together with minor alloying ingredients and incidental impurities, are characterized by being readily workable as compared to conventional casting alloys of the same chemical composition which are too brittle and have too little ductility to hot work.

4 Claims, No Drawings FULLY DENSE CONSOLIDATED-POWDER SUPERALLOYS The present invention relates to a workable nickel base superalloy and more particularly to a heat-resistant, highstrength, structural alloy of fully dense consolidated powder prepared from solidified powder particles featuring an ultraf'rne microstructure in which the secondary dendrite arrn spacing is less than about 0.0003 inch and in which the microsegregation of the consolidated alloy has been reduced to limits heretofore unattainable.

The utilization of high temperatures for many diverse operations has become an accepted part of the technology of modern industrial processes. Also, the quest for improved power sources has led to the development of such devices as superchargers, gas turbines, jet engines and the like all operat ing at elevated temperatures. These developments demand metals and alloys which will withstand prolonged exposure to temperatures well above about 1,300 F. and in many instances well above about l,700 F., and are capable of withstanding severe mechanical stress at these temperatures. In many instances it is desired that alloys for use in such apparatus be capable of being hot worked and machined, while in other instances the alloys may be employed in the form of castings. In any event such alloys must have high strength in order to be useful.

At the present time a number of relatively highly alloyed nickel base alloys, commonly referred to in the trade as superalloys, are commercially available. One such alloy commonly referred to as lN-100 has the following composition: about 0.15 percent carbon, about percent cobalt, about 10 percent chromium, about 5.5 percent aluminum, about 4.75 percent titanium, about 3 percent molybdenum, about 0.1 percent vanadium, about 0.015 percent boron, about 0.01 percent zirconium and the balance nickel with usual impurities in ordinary arnounts. Commercial alloys such as lN-100 have good oxidation resistance and retain fairly good strength values up to temperatures of 1,800 F. or even in some cases up to 2,000 F. These nickel base alloys are cast alloys which have relatively low ductility and accordingly are used in their as-cast shape.

Presently as-cast nickel base alloys which correspond compositionally to the alloys in the novel form of the present invention are characterized by relatively coarse dendritic structures which seriously detract from the physical and metallurgical properties of the materials. Because of this undesirable microstructure these alloys are brittle and extremely difficult to fabricate into useful shapes.

The present invention provides nickel base alloys in a novel form which overcome numerous shortcomings and disadvantages of previously known alloys and which have particular utility at high temperatures. Such alloys are considerably stronger than presently available cast alloys of similar chemical composition, but at the same time are readily fabricable into useful wrought forms.

Broadly stated, alloys of the present invention have the general composition range of:

Balance substantially nickel with residual impurities in ordinary amounts.

Preferred compositions for most applications in accordance with the present invention have the composition range of:

Percent by Weight About 0.15 to 0.20

Co About 13 to 17 Cr About 8 to l 1 Al About 5 to 6 Ti About 4.5 to 5.0 Mo About 2 to 4 Zr About 0.03 to 0.09 B About 0.01 to 0.02 V About 0.1 to 1.2

Balance substantially nickel with residual impurities in ordinary amounts.

The term balance essentially is used to include in addition to nickel in the balance of the alloy, small amounts of impurities such as sulfur, phosphorous, etc., and incidental elements such as niobium, tantalum, manganese, silicon, copper, iron, etc., in amounts which do not adversely affect the novel advantageous characteristics of the alloy.

Each of the superalloys provided by the present invention, though compositionally similar to certain alloys of the prior art, can be distinguished therefrom by its novel metallographic structure with the attendant increase in desirable mechanical properties. More specifically, each of the new nickel-base alloys is characterized by being readily workable.

Because of the high ductility of the unique ultrafine microstructure, the new nickel base alloys can be readily fabricated. into useful shapes and retain a large amount of the cold work induced during fabrication which improves the strength of the alloys.

In accordance with the present invention an atomized, prealloyed powder of the desired composition is first made by atomizing a molten alloy charge consisting essentially of the ingredients in substantially the proportions stated in the general compositions set out hereinabove. The molten alloy charge can be obtained, if desired, by melting a conventional casting alloy such as is disclosed in US. Pat. No. 3,061,426, patented Oct. 30, 1962, the disclosure of said patent being incorporated herein by reference. Accordingly, the alloys produced in accordance with the invention include a fully dense consolidated-powder alloy having the composition defined by any of claims 1-4 of US. Pat. No. 3,061,426, wherein the improvement comprises the hot workability of the alloy. The atomized alloy charge is then rapidly quenched to solidify the molten particles and prevent appreciable formation of coarse crystals of dispersed secondary phase in the resultant powder. The prealloyed powder is then compressed and mechanically hot worked to consolidate the powder into metal stock having a density substantially equivalent to the alloy in its cast state.

Nickel-base alloys with the composition set out in Table I were made according to this invention and compared with a prior art alloy of nearly identical chemical composition.

TABLE 1 ElrSS Prior Art (in-) carbon 0.15-0.20 0.15 cobalt 13-17 15 chromium 8-11 10 ,aluminum 56 5.5

titanignr 4.5-5.0 H 5: molybdenum 2-4 3 7 silicon 0.2 max. manganese 0.2 max. iron W 1 max. zirconium 0.03-0.09 0.01 boron 0.01-0.02 0.015 vanadium 0.1-1.2 nickel balance 7 balance Alloys to be atomized were heated to a temperature of about 200 to 300 F. above fusion temperature inan induction-heated magnesia crucible under an argon blanket. The molten metal was poured into a preheated zirconia-lined tundish which had a 3/ 16-inch opening in the bottom. The narrow stream of the molten alloy'charge from the tundish passed through the center of a mild steel. zirconia lined nozzle of A- mch-diameter opening and was atomized by a et of high pressure (350 psi.) argon just below the tip of the nozzle. The droplets of prealloyed atomized alloy were rapidly quenched by the inert gas and by a large reservoir of water in the bottom cf the atomizing chamber.

The atomized powder obtained was washed several times with acetone, dried and screened to +80 and -80 mesh size fractions. The 80 mesh portion was placed in an lnconel can for consolidation. The can was lined with a sheet of molybdenum to prevent bonding between the can and the power during consolidation and to facilitate removal of the can material after fabrication. The powders were packed into the can on a vibrating table to obtainas much settling as possible and then cold pressed at from to 30 t.s.i. After the lids were welded on, the cans were hammer forged from approximately 12 inches down to 0.5 inch in height at a temperature of approximately 2,050 F. Following reheating the resultant plate was hot rolled at the same temperature down to 3/ 16-inch plate using a 10 percent reduction in thickness for each rolling pass. The consolidated material was then air cooled to room temperature, the plates were annealed, the canning material stripped away and the wrought material sectioned for testing.

Metallographie observations were made on each batch of atomized powder and on each consolidated and annealed plate. Photomicrographs were taken at 1,000X so that micros tructural comparisons could be made between commercially produced and atomized and consolidated alloys. Tensile specimens were taken from the centennost portion of the lt'orged and rolled plate which represented the area of densest material. Room temperature tensile tests were performed at a strain rate of 0.05 inch per minute. Material for the test specimens was machined into sheet tensile specimens approximately 2 inch long (1 inch gauge length), 0.125 inch thick, snd 0.5 inch wide (0.20 inch in gauge section). The specimens were tested in the as-rolled condition without heat treatment. Ultimate tensile strength, 0.2 percent offset yield strength and percent elongation in a 1.0 inch gauge length. were determined from load-elongation curves and from measurements of the gauge length scribe marks on the broken tensile specimens. The results of these tests appear in Table II.

it will be seen from the foregoing table that at room temperature the tensile and 0.2 percent yield strengths of the stomized and consolidated alloy of the present invention are appreciably greater than the tensile and 0.2 percent yield strengths of these alloys produced in the conventional manner. i.e., cast. Metallographic observations showed that dendrite spacing of these atomized superalloys was 0.00005-00001 in comparison to conventionally melted and cast superalloys having dendrite arm spacing generally 0.005 and above.

What is claimed is:

1. A fully dense consolidated-powder alloy consisting essentially of:

carbon about 0.01 to 0.5 percent cobalt about 5 to 30 percent chromium about 6 to 12 percent aluminum about 4 to 9 percent titanium about 0.5 to 6.5 percent aluminum plus titanium about 8 to 12 percent molybdenum about 1 to 8 percent zirconium about 0.01 to 0.25 percent boronabout 0.001 to 0.1 percent vanadium about 0.2 to 2 percent and the balance nickel with usual impurities in ordinary smounts, said alloy being characterized by being readily bot workable.

.2. An alloy having the composition of the alloy of claim 1, prepared by consolidation of a powder in which the dendrite arm spacing is less than about 0.0003 inch.

.3. A fully dense consolidated-powder alloy according to claim 1, consisting essentially of:

carbon about 0. 15 to 0.20 percent cobalt about 13 to 17 percent chromium about 8 to 1 1 percent aluminum about 5 to 6 percent :itanium about 4.5 to 5.0 percent molybdenum about 2 to 4 percent silicon about 0.2 percent maximum manganese about 0.2 percent maximum ll'Ol'l about 1 percent maximum sirconium about 0.03 to 0.09 percent boron about 0.01 to 0.02 percent vanadium about 0.1 to 1.2 percent and the balance nickel with usual impurities in ordinary amounts.

it. A fully dense consolidated-powder alloy consisting essentially of:

carbon about 0.15 percent :obalt about 15 percent chromium about 10 percent .tluminum about 5.5 percent titanium about 4.75 percent molybdenum about 3 percent srrconium about 0.01 percent soron about 0.015 percent snd the balance nickel with usual impurities in ordinary .tmounts, said alloy being characterized by being readily tot workable.

s e I t it UNITED STATES PATENT OFFlCE CERTIFICATE @F QORREQHQN Patent No. 3,649,257 Dated March 14, 1972 Inventor(s) STEWART G FLETCHER It is certified that error appears in the above-identified patent and that said Letters Patent are herebv corrected as shown below:

Column 3, line 1, "nozzle of 1/4 inch" should read --nozzle of 3/4 inch--; line 11, "and the power" should read --and the powder" Signed and sealed this 3rd day of October 1972.

(SHALL Attest:

EDWARD MQFLETCHERJRQ ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents USCOMM-DC GOING-P09 w u 5. GOVERNMENT PRINTING OFFICE: I969 O-i66-I43A I OHM PO-105O (IO-69) UNITED STATES PATENT OFFHIE CERTIFICATE 0F CORREQTEON Patent No. 3 ,649,257 Dated M r h 4 7 Inventor s) STEWART G FLETCHER It is certified that error appears in the above-identified patent and that said Letters Patent are herebv corrected as shown below:

Column 3, line 1 "nozzle of 1/4 inch" should read --nozzle of 3/4 inch-; line 11, "and the power" should read --and the powder-- Signed and sealed this-3rd day of October 1972.

(SEAL) Attest:

EDWARD MQFLETCHERJR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents URM F0-105O (IO-6Q) USCOMWDC 603764209 U S, GOVERNMENT PRINYING OFFICE: I969 D-" 85 34 

2. An alloy having the composition of the alloy of claim 1, prepared by consolidation of a powder in which the dendrite arm spacing is less than about 0.0003 inch.
 3. A fully dense consolidated-powder alloy according to claim 1, consisting essentially of: carbon about 0.15 to 0.20 percent cobalt about 13 to 17 percent chromium about 8 to 11 percent aluminum about 5 to 6 percent titanium about 4.5 to 5.0 percent molybdenum about 2 to 4 percent silicon about 0.2 percent maximum manganese about 0.2 percent maximum iron about 1 percent maximum zirconium about 0.03 to 0.09 percent boron about 0.01 to 0.02 percent vanadium about 0.1 to 1.2 percent and the balance nickel with usual impurities in ordinary amounts.
 4. A fully dense consolidated-powder alloy consisting essentially of: carbon about 0.15 percent cobalt about 15 percent chromium about 10 percent aluminum about 5.5 percent titanium about 4.75 percent molybdenum about 3 percent zirconium about 0.01 percent boron about 0.015 percent and the balance nickel with usual impurities in ordinary amounts, said alloy being characterized by being readily hot workable. 